Abstract: Non-stressed moisture stored in soil,water consumption of crops and effective precipitation during crop growth period are the main factors affecting moisture supply to winter wheat.All these change with time,different relationships being manifest for different periods of time.Based on experimental data,the paper deals with the dynamic change of moisture for winter wheat,establishing equation,which more or less卜 completely reflects the contradictions between demand and supply of water in the entire growth period,thus revealing the time distribution and intensity of droughts.The Penman equation is coordinated with biological factors in presenting equation for forecasting droughts.Non-stressed moisture stored in soil is predicted by using both meteorological factors and factors related to the crops,which may also be applied to analysis ofregional droughts.